This invention relates to elevator controls and, in particular, to the car and hall call buttons activated for requesting elevator service.
The contactless touch button, consisting of a cold cathode gas tube, is a popular and widely used type of button, particularly because it has no moving parts. It is the subject of U.S. Pat. Nos. 2,525,767, 2,525,768 and 2,525,769. The button is activated in response to the capacitance between a metallic coating on the cold cathode tube and the user's finger. In installations using this button, a D.C. voltage is applied across the anode and cathode while, at the same time, it is floated on an A.C. voltage to enhance the capacitive coupling response needed to fire the tube. Typically, the D.C. voltage is about 135 volts and the A.C. float voltage is about 200 volts r.m.s. When activated, the tube conducts a D.C. current, which is used to generate a signal to activate the elevator controls located in a remote control room, while at the same time, it glows to provide a visual indication of a service request.
When the requested elevator service is supplied, an A.C. signal is transmitted to the button and where it is used to bias the tube into its nonconductive state. The tube thereupon ceases to glow, indicating that the requested service has been supplied.
Power for the tube is derived from the control room and is carried over three conductors. One conductor carries the positive D.C. voltage; a second provides a D.C. return and the third carries the reset signal and the D.C. control signal. In installations having several call buttons on a floor or in a car, known as multiriser systems, the buttons are connected in parallel so that activation of one button will activate the others.
In certain applications there is a need, however, to replace the touch type button with a mechanical type. It is desired, however, that the replacement use the existing wiring and, naturally, require little if any modification to the power supplies in the control room. This "retrofit" unit also needs to provide a visual indication of a request and also have about the same performance characteristics as the gas tube unit.
There are two particularly important constraints imposed upon the retrofit unit. First, it should generate essentially the same D.C. control signal, when activated, and respond to the same type of reset signal, so that modifications are not necessary to the control circuitry. Second, it should be usable in the multiriser systems, and provide the same performance in those installations.